Latent viruses pose a serious health problem because they continually re-infect their host. It is believed they do this via transcription of latency-associated transcripts (LATs), which produce RNAs that are not translated into proteins to lessen the chance of detection and/or elimination by the host immune system.
In humans, they include all of the herpes viruses, such as HSV-1, HSV-2, VZV, CMV, EBV, HHV-6, HHV-7 and HHV-8, for example. Other latent viruses include the human polyoma viruses (JC and BK viruses), adenoviruses and Human Immunodeficiency Virus (HIV). These viruses are associated with a number of clinical conditions including recurrent herpes labialis, such as cold sores or HSV-1; genital herpes, such as HSV-2; various types of cancer, such as EBV or HHV-8; multi-organ or systemic infections, such as CMV; progressive multifocal leukoencephalopathy, such as the JC virus and AIDS, for example.
One such latent virus is HSV-1, which causes herpes keratitis. HSV-1 infection of the corneal surface is perhaps the most serious of all HSV-induced diseases. This ophthalmologic disease is difficult to treat, recurs unexpectedly, and often leads to corneal scarring and blindness. There are approximately 20,000 new cases of herpes keratitis annually in the U.S. and 28,000 recurrent cases, leading to 6000 corneal transplants. It is a recurrent disease where HSV-1 reactivation in the ganglion leads to repeated infections in the cornea with subsequent scarring and opacity. Daily prophylactic acyclovir—an effective strategy for prevention of genital HSV-2 recurrences—is much less effective against HSV-1 ocular recurrences. A quantum leap in the ability to prevent ocular HSV-1 recurrences is greatly needed for these patients.
Another example of a latent virus is human papillomavirus (HPV) that is one of the most common sexually transmitted diseases in the world. Approximately 5.5 million new cases of sexually transmitted HPV are reported each year and it is estimated that at least 20 million Americans are already infected. More than 100 different types of HPV have been identified and approximately 30 of these are spread by sexual contact. Many types of HPV can cause cervical or genital cancer.
HPV can cause genital warts that often disappear without treatment but they almost always reoccur. Several treatment options exist but they are uncomfortable, expensive and a temporary measure. Creams, such as Imiquimod, podophyllin anti-mitotic solutions, podofilox solutions, fluorouracil cream or trichloroacetic acid may be applied to the lesions themselves. Other treatment options include cryosurgery, electrocautery, laser treatment or surgery. Additionally, the antiviral drug alpha interferon may be injected directly into genital warts but this therapy is extremely expensive and does not offer a reduced re-infection rate over other treatment options.
There are currently no permanent methods of disabling a latent viral infection. Current therapies merely stop replication of a few viruses but do not affect latent viruses themselves, thus allowing for recurrent viral infection. A direct method of permanently curing latent viral infections is greatly needed.